One of the defining characteristics of climate change is poorly appreciated by most people: the higher temperatures and other effects induced by increasing levels of carbon dioxide in the atmosphere will persist for a very long time. Scientists have long realized that carbon dioxide emitted during the burning of fossil fuels tends to linger in the atmosphere for extended periods, even for centuries. Over the last few years, researchers have calculated that some of the resulting changes to the earth’s climate, including increased temperature, are more persistent still: even if emissions are abruptly ended and carbon dioxide levels gradually drop, the temperature will stubbornly remain elevated for a thousand years or more. The earth’s thermostat is essentially being turned up and there are no readily foreseeable ways to turn it back down; even risky geoengineering schemes would at best offset the higher temperatures only temporarily.

It’s a shocking realization, especially given how little progress has been made in slowing carbon dioxide emissions. But it is precisely the long-term nature of the problem that makes it so urgent for us to limit emissions as quickly and radically as possible. To have a decent chance of meeting the widely accepted international goal of keeping warming at or below 2 °C, emissions need to be cut substantially over the next few years. By 2050 they must be reduced by half or more from 2009 levels.

The mismatch between when we need to act and when many of the benefits will accrue helps to explain why climate change is such a politically and economically thorny problem. How do you convince people and governments to invest in a far-off future? Clearly, it is not a problem that can easily be addressed by most politicians, given the immediate and pressing needs of their constituents. Because it involves defining and understanding our responsibilities to future generations, our action (or inaction) on climate change falls squarely into the realm of moral and political philosophy.

Over the last few years a small but growing number of writers have begun to wrestle with some profound questions. What ethical guidelines should economists follow when evaluating today’s costs against future benefits? How should we weigh uncertainties, including the risks of catastrophic changes wrought by global warming? Would geoengineering be ethical? How does climate change affect our perception of the world and our future role in it? The conclusions they’ve reached are nuanced and can turn on esoteric definitions of terms such as “justice” and “moral good.” But their reasoning often provides keen insights into today’s most pressing policy questions.

In Climate Matters: Ethics in a Warming World, John Broome, a moral philosopher at the University of Oxford, explains the methods and arguments that help us understand the ethical implications of global warming, and he demonstrates why this reasoning can offer useful insights into how we should act. Trained in economics at MIT, Broome is particularly interested in assessing the ethical judgments made by economists. “Economists recognized, say, 50 years ago that economics is based on ethical assumptions,” he says. “But a number of them seem to have forgotten that in recent decades. They think what they do is somehow in an ‘ethic-free zone.’ And that plainly isn’t so. And climate change makes that obvious.”

One of the most controversial issues in economic analysis of climate-change policy is how to weigh the cost of implementing changes now against the benefits that future generations will realize—or the harm they will avoid. It might be supposed that we should do everything we can possibly do now, but that would probably be wrong, suggests Broome, since extremely radical action would have such negative consequences for those alive today that the effects would be felt for generations. Broome wrestles with how to balance these factors in an ethically responsible way, concluding that economists are, in general, right in adopting so-called cost-benefit analyses to evaluate actions on climate change. But he stresses that the ethical assumptions underlying such analyses are critical—and that economists often ignore or misunderstand them.

Even if people are richer in the future, climate change might reduce the quality of their lives.

A standard tool in cost-benefit analysis is what economists call the discount rate, which makes it possible to apply a value today to an investment that won’t pay off until some future date. In Broome’s example, if the discount rate is 6 percent per year, you could buy a given amount of rice now, but you should pay 94 percent of that price today if it were to be delivered in a year or 83.06 percent if it were to be delivered in three years. The basic idea is that people will be richer in the future as economies keep growing, so a given amount of a commodity or money will have less value than it has now. The higher the discount rate, the less value is assigned to a future commodity.

The way economists calculate discount rates has enormous implications for energy policy. In 2006, Nicholas Stern, a prominent economist at the London School of Economics and former chief economist of the World Bank, published “The Economics of Climate Change,” an influential report that called for immediate and significant spending (he has more recently called for even larger investments; see “Q&A with Nicholas Stern.”) Stern used an unconventionally low discount rate of 1.4 percent, which led him to place a high value on the future benefits of today’s investments to address climate change. He was immediately attacked by a number of academic economists. Most notably, William Nordhaus of Yale University published A Question of Balance, in which he argued that the appropriate discount rate should be about 5 percent. Nordhaus thus concluded that spending to deal with climate change should be much more gradual, and that much of it should be delayed for several decades.

Typically, economists calculate the discount rate by using money markets to determine the expected return on capital. The reasoning is that the market is the most democratic means of assigning value. But while that practice might work well to account for the value of commodities, Broome argues that calculating the discount rate for action on climate change is far more complex. For one thing, the conventional method doesn’t fully account for the possibility that even if people are richer in the future, climate change might reduce the quality of their lives in other important ways—and thus it underestimates the value of current investments. Broome ends up supporting a rate similar to Stern’s.

But his larger point is, more simply, that even such quantitative economic evaluations need to fully incorporate moral principles.

The discount rate is a matter of the value of future people’s benefits compared to our own. More than anything else, it determines what sacrifices the present generation should make for the sake of the future. This is a moral matter.

Broome also ponders the implications of how we think about extreme risk. Most people accept that it is worthwhile to invest in avoiding a particularly onerous outcome, even if it is not a likely one. That’s why we buy fire extinguishers and home fire insurance, even though a fire is unlikely. But how should we value the ability to avoid a catastrophic outcome that is very improbable? Some leading economists have begun arguing that heading off even the remote chance of such outcomes should be the main object of climate-change policy. Not surprisingly, Broome calls for using moral principles to evaluate just how bad various outcomes could be and how much we should concentrate on avoiding them. That means making difficult decisions about the value of human lives and of natural systems; it also means calculating how “bad” it would be if climate change reduced the size of the human population. “Deciding whether it will be very, very bad takes ethical analysis,” he says.

Broome’s focus on the reasoning of economists is not arbitrary. Economists have “largely been in the driver’s seat” in guiding governments’ policies on climate change, he says. “But they don’t always get their ethical foundations right.” By not fully accounting for people’s future well-being and such difficult-to-quantify values as the beauty of nature, Broome says, many economists have seriously underestimated how much we should be spending now to address climate change.

What Would God Do?

In his 2010 book, Requiem for a Species: Why We Resist the Truth about Climate Change, Clive Hamilton, a professor of public ethics at Charles Sturt University in Canberra, Australia, argues that it is already too late to stop many of the dire consequences of global warming and that we’re almost sure to make it far, far worse.

After that book was published, ­Hamilton says, he became convinced that the “growing gap” between the widely accepted scientific evidence for the dangers of global warming and the lack of any political progress toward addressing the problem would increase the pressure to view geoengineering as a feasible option. He expects it to become “the dominant issue in climate-change discussions within the next five to 10 years.” So in his newest book, Earthmasters: The Dawn of the Age of Climate Engineering, ­Hamilton takes a critical look at various geoengineering proposals, such as the use of sulfur particles or manmade materials to partially block the sun (see “A Cheap and Easy Plan to Stop Global Warming.”) He is highly skeptical of any such schemes to rejigger the earth’s atmosphere to fix climate change and deeply suspicious of the motivations of many of its advocates.

Hamilton uses the term “playing God” to describe the hubris of some of the people suggesting geoengineering. He doubts we would be very good at it, or very fair in applying a technology that would be likely to harm some people and help others. Perhaps most damning, he says that it raises moral problems—and strains common sense—to propose using such risky measures because we have failed to tackle climate change with existing technologies.

If humans were sufficiently omniscient and omnipotent, would we, like God, use climate engineering methods benevolently? Earth system science cannot answer this question, but it hardly needs to, for we know the answer already. Given that humans are proposing to engineer the climate because of a cascade of institutional failings and self-interested behaviours, any suggestions that deployment of a solar shield would be done in a way that fulfilled the strongest principles of justice and compassion would lack credibility, to say the least.

In Hamilton’s thinking, geoengineering is the latest example of our hope that “techno-fixes” will rescue us from global warming. He points to large—and, he says, largely fruitless—investments in carbon capture and storage (CCS) as a way to negate the emissions from burning coal and writes that the “false promise” of CCS has contributed to a “lost decade in responding to climate change.” The problem is not only that such “energy miracles” are unlikely to work as advocates hope but that the prospect of them presents a moral hazard, tempting people to persist in risky actions without expecting dire consequences. What’s more, says ­Hamilton, relying on techno-fixes ignores the underlying economic, political, and ethical failures that have produced the climate-change crisis in the first place.

More broadly, Hamilton emphasizes the “astonishing ethical implications” of climate change over the long term—and of what would-be geoengineers are proposing. We’re at “a historical point,” he says. “We need to reopen the question of who we are as a species and what kind of a creature we have become.” Yet the attentive reader will note that Hamilton doesn’t rule out geoengineering in the future, if the situation becomes desperate. Rather, he calls on us to examine the economic and political motivations of geoengineering advocates and to understand that trying to engineer the climate reflects a misplaced faith in technology’s ability to solve political and social problems.

We have barely begun to grapple with the moral issues related to climate change.

In A Perfect Moral Storm: The Ethical Tragedy of Climate Change, Stephen M. Gardiner reaches similar conclusions after a far different type of analysis. Unlike Hamilton, Gardiner, a professor of philosophy at the University of Washington, has little interest in the players and politics behind geoengineering. Instead, he rigorously analyzes the moral justifications for considering the technology.

In particular, he questions the simplistic reasoning that since geoengineering could turn out to be the “lesser evil” in some future climate emergency, we should be researching it now to understand the technology and its risks. That argument conceals many ethical challenges, he contends. Is it ethical of us to expect a future generation to take on the dangers and costs of geoengineering because we have failed to address climate change? And wouldn’t a large research push on geoengineering just increase the unfortunate possibility that it will be used?

Crosswinds

Though they reflect very different interests and objectives, these books, taken together, begin to shed light on why climate change has been such a difficult problem to address and even define. After all, if it is fundamentally a moral issue, then simple economic or technology-based solutions will understandably fall short.

What’s more, climate change poses particularly tough moral problems. The title of Gardiner’s book refers to the convergence of three separate moral “storms,” or “obstacles to our ability to behave ethically.” The biggest is the way future generations are at the mercy of current ones —what he sometimes calls generational buck-passing. The others involve the different impacts of climate change around the world and among different populations, and the prospect that theoretical uncertainties in areas such as intergenerational ethics and climate science will make it difficult for us to act. Gardiner spends nearly 500 pages trying to map the crosswinds of these storms, concluding that “it will not be easy for us to emerge morally unscathed.”

Still, a clear first step would be to acknowledge the moral issues associated with climate change and the likely need for some painful decisions. Gardiner rightly points out that much of the public debate is dominated by “technological and social optimists” who argue for “win-win” solutions that will allow us to address the problem without any economic sacrifices or hard ethical choices. Might green energy simply solve the problem, not only for us but for future generations? We’re beginning to know the answer; a clean-tech revolution hasn’t come close to happening, in part because it would necessarily mean making difficult choices. What’s more, says Gardiner, clinging to that hope obscures the real reasons we need to do something about climate change:

More generally, the current focus on the green energy revolution rationale puts pressure in the wrong place. The dominant reason for acting on climate change is not that it would make us better off. It is that not acting involves taking advantage of the poor, the future, and nature … The green revolution claim runs the risk of obscuring what is at stake in climate change, and in a way that undercuts motivation. The key point is that we should act on climate change even if doing so does not make us better off: indeed, even if it may make us significantly worse off. If we hide or dilute the moral issues, then this important truth is lost, and the prospects for ethically defensible action diminish.

We have barely begun to grapple with the moral issues related to climate change. Indeed, few are even likely to accept the basic role that ethical issues should play in our policy decisions, and certainly our responsibilities to the distant future are seldom part of the public debate. But given the convincing evidence climate scientists have presented that our actions over the next several decades will have direct consequences for generations who will live many years from now, we must consider the moral dimensions of our response. As Gardiner puts it at the end of his book: “The time to think seriously about the future of humanity is upon us.”